1. Field of the Invention
The present invention relates to a method of producing a metallic thin film, for example, a thin film formed on a substrate by using noble metal alkoxides alone or metal alkoxides with noble metal oxides as the main components on additives to thereby improve a pH-response sensor, a hydrogen sensor, a gas sensor, and other various types of applications.
2. Description of Related Art
Various methods have been known in the conventional art for applying a thin film to a substrate. For example, an evaporation method wherein a target is set within a vacuum bell jar has been utilized with the target being heated to a vaporization temperature to permit the resulting vapors to stick to a substrate, thereby forming a thin film. Additionally, a sputtering method wherein a target within a vacuum environment is struck, for example, by a glow discharge to thereby form a thin film on a substrate. An additional method of applying a thin film coating to a substrate is known wherein a metallic melt is prepared and a substrate is then immersed in the metallic melt to form a thin film followed by a subsequent drying and baking step. These methods of forming a thin metallic film are only illustrative of the attempts that have been made in the prior art.
A vapor deposition method or a sputtering method has frequently been found advantageous in permitting a uniform thickness of a thin film to be applied relatively free of impurities. The sputtering method is particularly suitable for a high melting point substance, for example, oxides. Problems have occurred, however, when a thin film is to be formed within a vacuum bell jar, since relatively complicated and expensive apparatus are required. In addition, if a metal oxide is selected as a target, it is usually necessary to regulate the purity of the oxide and if the target is porous, pretreatment is frequently required. Problems frequently occur when a thin film is to be made of multi-component metals or metal oxides and it is necessary to provide various kinds of targets in order to vapor-deposit or sputter the various materials from those targets simultaneously or sequentially with additional cost involved in the apparatus and procedure.
With the advent of inexpensive microcomputer systems capable of analyzing sensor information, for example, in the automotive environment, a need has been created for providing fairly inexpensive sensors. Accordingly, the prior art is still seeking to optimize the preparation of coating substrates with thin metallic films in an economical manner.